facebook javascript login dirty check

lisp

(defparameter *facebook-app-id* "id")                                                                                                          
(defparameter *facebook-app-secret* "secret")                                                                                     
                                                                                                                                                            
(defun facebook-login-p ()                                                                                                                                  
  (let ((kvs (sort (map 'list (lambda (kv)                                                                                                                  
                                (split-sequence:split-sequence #\= kv))                                                                                     
                        (split-sequence:split-sequence #\& (string-trim (list #\") (hunchentoot:cookie-in (format nil "fbs_~A" *facebook-app-id*)))))       
                   (lambda (a b)                                                                                                                            
                     (string<= (car a) (car b))))))                                                                                                         
    (let ((sig (find-if (lambda (kv) (string= (car kv) "sig")) kvs))                                                                                        
          (new-kvs (remove-if (lambda (kv) (string= (car kv) "sig")) kvs)))                                                                                 
      (string-equal (car (cdr sig)) (ironclad:byte-array-to-hex-string                                                                                      
                                     (md5:md5sum-sequence                                                                                                   
                                      (concatenate 'string (reduce (lambda (a b)                                                                            
                                                                     (concatenate 'string a b))                                                             
                                                                   (loop                                                                                    
                                                                      for kv in new-kvs                                                                     
                                                                      collect                                                                               
                                                                      (concatenate 'string (car kv) "=" (car (cdr kv)))))                                   
                                                   *facebook-app-secret*)))))))